Police said two people were stabbed and one person was shot during a violent weekend in Brockton. A 68-year-old man was stabbed in the back during an attempted robbery at about 8 p.m. Saturday, police said. The man was taken to a Boston hospital; his injuries were not considered life-threatening. Police told The Enterprise that an 18-year-old man was shot just after 2 a.m. Sunday, and there was another stabbing Sunday afternoon. The shooting victim was taken to a Brockton hospital with injuries not considered life threatening. Police have not announced any arrests.